This invention relates to improvements in hydraulic apparatus having telescopic cylinders for reaching comparatively long distances relative to the length of the cylinders. Telescoping cylinder apparatus are especially useful in elevator installations. Elevators of the hydraulic type usually have the capacity to extend upwardly a considerably greater distance than the length of any one hydraulic cylinder. This is accomplished by using a telescopic hydraulic cylinder apparatus including a base cylinder, one or more intermediate cylinders, and a piston rod, all of which extend outwardly from the upper end of the base cylinder, each successively smaller and telescopically arranged within the next larger cylinder.
An example of an apparatus of this type is contained in Canadian Pat. No. 727,962 to Richard E. Atkey, which shows and describes a telescopic hydraulic cylinder apparatus designed so that all the moving cylinders and the piston rod move simultaneously outwardly and inwardly relative to the respective cylinders in which they operate. This type of device obviated many of the disadvantages of prior art telescoping hydraulic devices inasmuch as simultaneous movement resulted in a constant speed during operation. In many prior forms of telescopic hydraulic cylinder apparatus, the individual hydraulic cylinders would operate successively rather than concurrently, resulting in jerking movements and changes in speed as each cylinder reached the end of its stroke. This rendered such devices unsuitable for elevator applications.
In the Atkey device, simultaneous movement of the telescoping members occurs in that in between each adjacent pair of telescopic cylinders, or cylinder and piston rod, a piston is attached to the lower end of the smaller member, and an annular seal is attached to the larger member, the seal receiving the smaller member in sliding, sealing relation. The apparatus is operated by pumping hydraulic fluid into the base cylinder below the innermost intermediate cylinder to force that cylinder upwardly. In normal operation, no fluid flows from the lower chamber, into which this fluid is pumped, into the upper chamber containing the intermediate cylinders and the piston rod. The telescoping arrangement of the upper components will result in their outward movement when the first intermediate cylinder is moved upwardly due to a change in the volume configuration of the upper components, that is, the reduction in volume between adjacent cylinders when the pistons are moved upwardly relative to the annular seal.
When applying the above-described telescoping cylinder apparatus to elevator applications, an annoying problem occurs. In the normal operation of the elevator, some leakage is expected at the region of the hydraulic seals between the telescoping cylinders. Such leakage causes the piston rod to settle toward the bottom of the apparatus. Also, after some leakage, the intermediate pistons upon extension will strike their upper limit points before the piston rod is fully extended, and thus the elevator may have trouble reaching the top floor. In practical operation, a passage is provided between the lower chamber and upper chamber and the piston rod will continue to extend upwardly as replacement fluid is forced through the passage, but only after a considerable jar. Also, a considerably higher pressure is required in that the piston rod has a much smaller transverse area upon which the fluid acts. In the opposite direction, when the cylinders are retracting back into the base cylinder, the piston rod will fully retract and strike the adjacent intermediate cylinder before the intermediate cylinders are fully retracted. Again it is true that the intermediate cylinder will continue to retract and lower the elevator to its lowest floor, but only after a considerable jarring of the elevator, and at a considerably reduced speed since the piston rod is not moving with respect to the intermediate cylinder. The problem in both cases results from a loss of hydraulic fluid in the annular chambers between each of the adjacent intermediate cylinders due to leakage.